This application is based on Application No. HEI 10-221297 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a halftone dot image discrimination method and image processing device applicable to digital copiers and the like.
2. Description of the Related Art
In digital copiers and the like, image data obtained by reading a document are subjected to various image processing in accordance with the type of document image. Types of document images include, for example, text images, variable density images, halftone dot images and the like, and in order to discriminate these image types, the document image is divided into small block areas. For example, to discriminate whether or not an image is a halftone dot image, the halftone dot image discrimination must be performed on each block area.
Conventionally, the methods often used to discriminate a halftone dot image determine whether or not the number of white or black isolated points within a block area exceeds a threshold value. The discrimination result is output as a halftone dot discrimination signal representing whether or not the block area is a halftone dot area. Image processing (smoothing process) is performed to prevent moire in the halftone dot image based on the halftone dot discrimination signal.
In the conventional halftone dot image discrimination methods mentioned above, discrimination simply determines whether or not an image is a halftone dot image regardless of whether the image is a monochrome image (black and white) or color image. As a result, the smoothing process is performed based on the obtained halftone dot discrimination signal.
When the smoothing process is performed, however, the color component tends to enlarge and extend beyond the edge area of the halftone dot image. Accordingly, there is concern of color bleeding through the edge area so as to adversely affect the reproducibility of black color. Furthermore, when the halftone dot image is a color image, there is concern that color muddiness may occur in the edge area due to the smoothing process, thereby reducing the vividness of the color.
An object of the present invention is to eliminate the previously described disadvantages.
Another object of the present invention is to provide a halftone dot image discrimination method and image processing device for suitably processing monochrome and color halftone dot images, respectively, when performing image processing on halftone dot images.
Still another object of the present invention is to provide a halftone dot image discrimination method and image processing device which prevent color bleed and muddiness.
These and other objects are attained by an image processing device having a halftone dot image discrimination unit for discriminating whether or not an image contained in a predetermined area is a halftone dot image, a color/monochrome discrimination unit for discriminating whether or not an image contained in the predetermined area is a color image or a monochrome image, a first image processor for executing a first image process on the image contained in the predetermined area when the image contained in the predetermined area is a halftone dot image and a color image, and a second image processor for executing a second image process on an image contained in the predetermined area when the image contained in the predetermined area is a halftone dot image and a monochrome image.
The objects of the present invention are further attained by an image processing device having, a divider for dividing image data into blocks, a halftone dot image discrimination unit for discriminating whether or not the image contained in each block is a halftone dot image, a color/monochrome discrimination unit for discriminating whether or not the image contained in each block is a color image or monochrome image, a first image processor for executing a first image process on the image contained in a block when the image contained in that block is a halftone dot image and a color image, and a second image processor for executing a second image process on the image contained in a block when the image contained in that block is a halftone dot image and a monochrome image.